1. Field of the Invention
A hydraulic mount apparatus for supporting a vibration source.
2. Description of the Prior Art
Conventional hydraulic mounts exist for supporting and providing vibration isolation of vibration sources. One well known application of these mounts is for supporting components of automotive vehicles. These mounts typically operate to provide engine vibration isolation while also controlling the motion of the engine and connected powertrain components with respect to the vehicle frame or body structure. In many applications of engine and powertrain mounts, it is desirable to vary damping characteristics of the mount to provide selective isolation of vibrations at certain frequencies. At the same time, it is necessary to provide the mount with a relatively high dynamic stiffness to control large displacements of the powertrain with respect to the vehicle body structure.
Magnetorheological fluid-based vibration damping mounts have been developed to isolate or dampen vibrations at multiple frequencies. Magnetorheological fluid, as known in the art, is responsive to a magnetic field to modify its shear properties. Specifically, it has the ability to reversibly change from a free-flowing, linear, viscous liquid to a semi-solid with controllable yield strength when exposed to a magnetic field. These magnetorheological fluid-based dampers use this characteristic of the fluid to control the spring and damper rates when required.
One such magnetorheological fluid based mount is disclosed in U.S. Pat. No. 6,622,995 to Baudendistel et al. The mount includes a housing that extends about and along a first axis and defines a housing chamber. A flexible body made of an elastic material is disposed in the housing chamber and extends radially about and along the first axis for deforming elastically in response to movement of a vibration source (i.e. engine of an automotive vehicle) relative to a base (i.e. frame of the automotive vehicle). Further, a diaphragm made of an elastic material is disposed in the housing chamber and spaced axially from the flexible body. A partition assembly is disposed in the housing chamber between the flexible body and the diaphragm for dividing the housing chamber into a pumping chamber between the flexible body and the partition assembly, and a receiving chamber between the partition assembly and the diaphragm. The volume of each of these chambers is changed by deformation of the flexible body and the diaphragm in response to an external excitation. A sensor is disposed on the automotive vehicle for measuring a vibration condition of the automotive vehicle in response to the external excitation and producing a corresponding signal. Magnetorheological fluid is contained within the pumping and receiving chambers. The partition assembly defines a fluid passage that extends axially between the pumping chamber and the receiving chamber to fluidly connect the pumping chamber and the receiving chamber for passing the fluid between the pumping and receiving chambers in response to deformation of the flexible body and the diaphragm. The partition assembly includes an electromagnet coil disposed adjacent to the fluid passage for variably generating a magnetic flux across the fluid passage for modifying the shear resistance of the magnetorheological fluid passing through the fluid passage to variably change the damping stiffness of the mount in response to the signal from the sensor.
A common shortcoming of magnetorheological fluid-based mounts is that their vibration isolating capabilities are limited to isolating vibrations at relatively low frequencies, typically less than approximately 20 Hz, because the magnetorheological fluid is unable to pass through the fluid passage at higher frequencies.
In order to combat this shortcoming, a hybrid mount disclosed in Young-Min Han et al., Design and control of a hybrid mount featuring a magnetorheological fluid and a piezostack, 20 Smart Mater. Struct. 075019 (2011), was developed to reduce vibrations in a larger frequency range. The hybrid mount includes a magnetorheological fluid damping system to reduce vibrations at relatively low frequencies, and a piezostack actuator that excites a secondary inertial mass such that the inertial forces of the secondary mass substantially cancel the forces from the external excitation to cancel relatively high frequency vibrations. However, a downside to this system is that the secondary mass and piezostack actuator have to be sized properly in order to cancel the forces from the external excitation, resulting in the addition of undesirable extra mass to the system.